Microbiology and Immunology - Repository Poltekkes Kaltim

The second edition of the Textbook of Microbiology and Immunology has been thoroughly revised and updated to incorporate the latest information in the field of medical microbiology. I welcome reader's opinions and suggestions for further improvement of the book in the future edition.

GENERAL MICROBIOLOGY

SECTION II IMMUNOLOGY

SECTION III BACTERIOLOGY

SECTION IV VIROLOGY

SECTION V MYCOLOGY

SECTION VI APPLIED MICROBIOLOGY

Introduction

Historical Background

Microorganisms as a Cause of Disease

Chapter 43

Chapter 1

Antony van Leeuwenhoek: The Microscopist

Theory of Spontaneous Generation

Louis Pasteur: Father of Microbiology

S ection III Chapter 43

Robert Koch: The Founder of Koch’s Postulates

The microorganism must be present in every case of the disease but absent from healthy host
The suspected microorganism must be isolated and grown in a pure culture from lesions of the disease
The isolated organism, in pure culture, when inoculated in suitable laboratory animals should produce a similar
The same microorganism must be isolated again in pure culture from the lesions produced in experimental

The same microorganism must be re-isolated in pure culture from the lesions produced in experimental pure culture from the lesions produced in experimental animals. The specific antibodies against the bacteria must be detectable in the serum of a patient suffering from the disease.

Self-Experimentation Studies

He developed the pour plate method and was the first to use solid culture media for cultivating bacteria. A golden age of about 30–40 years followed in which most of the major bacterial pathogens were isolated.

Study of Viruses

Most human bacterial pathogens meet Koch's postulates, except those of Mycobacterium leprae and Treponema pallidum, the causative agents of leprosy and syphilis, respectively. The term virus (taken from the Latin for slimy fluid or poison) was used interchangeably at that time for any infectious agent and was thus applied to TMV and subsequently to all agents of the class.

Loeffler and Frosch (1898) described and isolated the first filterable agent from animals, the foot-and-mouth disease virus of cattle. Walter Reed and his team in Cuba (1902) recognized the first filterable human virus, yellow fever virus.

Phenomenon of Immunity

Mechanisms of Immunity

Speciﬁ city of the Antibody Molecule

The selective theory: The earliest conception of the selective theory dates to Paul Ehrlich in 1900. In the

The instructional theory: According to the instructional theories, a particular antigen would serve as a template

The clonal selection theory: The instructional theories were formally disproved in the 1960s, during which

Chemotherapeutic Agents

Antibiotics

Eukaryotes: Fungi, algae other than blue green, protozoa, and slime moulds are eukaryotes

Size of Bacteria

Microscopy

Types of Microscopy

Bright-field microscopy: Bright-field microscopy (always referred to as ordinary light microscopy) is the most common

The wet preparation is also useful for the demonstration of microorganisms in urine or feces, and also for the detection of fungi in the skin. It is also useful to measure the approximate size of the bacteria, fungi and protozoa in stained preparations.

Dark-ground microscopy: The dark-ground microscopy makes use of dark-ground microscope, a special type of

Dark Earth Microscopy: Dark Earth Microscopy uses dark-stained microscopy, a special type.

Phase-contrast microscopy: Phase-contrast microscopy makes use of a specific optical system that converts differences

S ection III Chapter 43Section IChapter 2

Interference microscopy: This is another specialized appli- cation of light microscopy used for demonstrating cell organ-

Scanning electron microscopy is another development that provides a three-dimensional image of an object and high resolution. This method is useful for studying the cellular ultrastructure of microorganisms in the living state.

Study of Bacteria

This method is based on rapid cooling of samples by deep freezing in liquid gas and the subsequent formation of carbon platinum replica of the sample. Confocal microscopy: It is useful for obtaining high resolution images and for three-dimensional reconstruction of biological models.

Staining Methods

The pus cells and epithelial cells present in the smear, on the other hand, take on the blue color of the counterstain and appear blue. Acid fastness is due to (a) the high content of lipids, fatty acids, mycolic acid components and (b) higher alcohols found in the Mycobacterium cell wall.

Shape of Bacteria

Cocci: The cocci (kokkos, berry) are oval or spherical cells

The decolorizing agent, such as acetone or ethanol, used during staining disrupts this membranous coat, and the dye and iodine complex is washed out by gram-negative bacteria. There are certain groups of bacteria, such as Mycobacterium tuberculosis and Mycobacterium leprae, that cannot be considered typical Gram-negative or Gram-positive bacteria.

Structure and Functions of Bacterial Cell Envelope

Cell Wall

Teichoic acids: Teichoic acids are polymers of polyribitol phosphate or polyglycerol phosphate containing ribitol and
Teichuronic acid: Teichuronic acid consists of repeat units of sugar acids (such as N-acetylmannuronic or D -glucuronic
Cell wall deficient forms: The cell wall could be removed by hydrolysis with lysozyme or by blocking peptidoglycan
Pleomorphic bacteria: Pleomorphic bacteria (e.g., Yersinia pestis) may show considerable variation in size and shape called
Involution forms: The involution forms are those that on ageing of culture show swollen and aberrant forms, especially

Lipopolysaccharides: Lipopolysaccharides (LPS) are complex molecules present in the outer membrane of the Gram-negative bacteria. There is little variation in the structure of lipid A among different species of the gram-negative bacteria.

Cell Membrane

Protoplasts: These are defective unstable forms of bacteria with an intact cytoplasmic membrane but without any cell wall. Spheroplasts: These are defective forms derived from Gram-negative bacteria in the presence of EDTA (ethylenediaminetetraacetic acid).

Cytoplasm

Pleomorphic bacteria: Pleomorphic bacteria (eg Yersinia pestis) can show considerable variation in size and shape called pestis) can show considerable variation in size and shape called pleomorphism. The cell walls can be demonstrated by (a) differential staining procedure, (b) electron microscopy, (c) plasmolysis, (d) microdissection, (e) mechanical disruption of the cell, and (f) serological test by exposure to specific antibodies.

Nucleus

Capsule and Slime Layer

Surface Appendages

These are usually composed of a single type of protein molecule, sometimes with carbohydrates attached. A specialized type of pili called sex pili are responsible for the attachment of donor and recipient cells in bacterial conjugation.

Sporulation

The spores can vary between different species depending on the position, shape and relative size of the spores. The spores of Bacillus stearothermophilus are used as an indicator of proper sterilization by autoclaving.

Growth and Multiplication of Bacteria

Demonstration of Spores: Spores can be observed simply as intracellular refractile bodies in unstained cell suspensions or as colorless areas in cells stained by conventional methods, such as Gram stain. When stained with modified ZN stain (with 0.25-0.5% sulfuric acid instead of 20% sulfuric acid), the spores appear as red acid-solid bodies.

Generation Time

For example, spores may be central, subterminal, or terminal; may be oval or spherical in shape; and may be bulging or non-bulging.

Bacterial Count

In the plate method, the sample is diluted and a small amount spread over the surface of the agar plate. The number of colonies that grow after an appropriate incubation time indicates the number of viable bacteria.

Bacterial Growth Curve

Stationary phase: After log phase, the bacterial growth almost stops completely due to lack of essential nutrients, lack of water

Factors Affecting Growth of Bacteria

Microaerophilic bacteria - those bacteria that can grow in the presence of low oxygen and in the presence of a low (4%) concentration of carbon dioxide (eg Campylobacter jejuni). Anaerobic bacteria: Obligate anaerobes are bacteria that can only grow in the absence of oxygen (eg Clostridium botulinum Clostridium tetani etc.).

Bacterial Nutrition

Consequently, factors such as osmotic pressure and salt concentration of the solution affect the growth of bacteria. Sudden exposure of bacteria to hypertonic solution can cause osmotic withdrawal of water, leading to osmotic shrinkage of the protoplasm (plasmolysis).

Deﬁ nition of Frequently Used Terms

Sterilization

Physical methods of sterilization, and 2. Chemical methods of sterilization

Physical Methods of Sterilization

Sunlight 2. Heat

Sound (sonic) waves

S ection III Chapter 43Section IChapter 3

Sterilization at a temperature ⬍100°C: Pasteurization is an example of sterilisation at a temperature ⬍100°C
Sterilization at a temperature of 100°C: Sterilsation at a temperature of 100ºC includes (a) boiling and (b) steam
Sterilization at a temperature > 100°C: This method is otherwise known as sterilization by steam under pressure
Flaming: Sterilization of inoculating loop or wire, the tip of forceps, searing spatulas, etc., is carried out by holding
Incineration: Incineration is an excellent method for safely destroying infective materials by burning them to
Hot-air oven: The hot-air oven provides another means of dry heat sterilization and is the most widely used method
Depth filters: Depth filters consist of fibrous or granular materials that have been bonded into a thick layer filled with
Membrane filters: Membrane filters are made up of (a) cellulose acetate, (b) cellulose nitrate, (c) polycarbonate, (d)
Ionizing radiations: Ionizing radiation is an excellent sterilizing agent with very high penetrating power
Nonionizing radiations: Nonionizing radiations include infrared and ultraviolet radiations

It is useful for sterilizing materials that cannot withstand the higher temperature of the hot air oven. Sterilization Controls: Various sterilization controls are used to determine the effectiveness of sterilization by moist heat.

Chemical Methods of Sterilization

Infrared radiation is used for rapid and mass sterilization of disposable syringes and catheters. Biological controls used to test the efficacy of sterilization techniques are summarized in Table 3-3.

Disinfection

It kills most vegetative bacteria, but not spores, which are highly resistant to this radiation. Heat generated by the sonic waves (up to 80°C) also appears to contribute to the antimicrobial action.

Properties of Ideal Disinfectant

Ideally, the disinfectant should have a wide spectrum of antimicrobial activity. It must be effective against a wide
It should act in the presence of organic matter
It should be stable upon storage and should not undergo any chemical change
It should be odorless or with a pleasant odor
It should be soluble in water and lipids for penetration into microorganisms
It should be effective in acidic as well as in alkaline media
It should have speedy action
If possible, it should be relatively inexpensive

Because UV radiation tends to burn the skin and cause damage to the eyes with prolonged exposure, UV lamps should be turned off when people are working in such areas. Ultrasonic devices are used in dental offices and some medical practices to remove dirt and saliva from instruments before sterilization and to clean dental restorations.

Action of Disinfectants

They produce damage to the cell wall and alter permeabil- ity of the cell membrane, resulting in exposure, damage, or
They alter proteins and form protein salts or cause coagu- lation of proteins
They inhibit enzyme action and inhibit nucleic acid syn- thesis or alter nucleic acid molecules
They cause oxidation or hydrolysis

In practice, this balance between effectiveness and low toxicity for animals proves difficult to achieve.

Factors Inﬂ uencing Activity of Disinfectants

Types of Disinfectants

Anionic surface active agents: These include soaps prepared either from saturated or unsaturated fatty acids, which act

Soaps prepared from saturated fatty acids are more effective against gram-negative microorganisms, and those prepared from unsaturated fatty acids are more effective against gram-positive bacilli and Neisseria.

Nonionic surface active agents: These are nontoxic and some of them may even promote the growth of bacteria

Amphoteric or ampholytic compounds: These are active against a wide range of Gram-positive and Gram-negative

Acids (such as sulfuric acid, nitric acid, hydrochloric acid and benzoic acid) and alkalis (such as potassium and sodium hydroxide and ammonium hydroxide) are bactericidal in nature. Organic acids are widely used in food preservation because they prevent spore germination and bacterial and fungal growth, and because they are generally considered safe to eat.

Testing of Disinfectants

He developed the pour plate method and was the first to use solid culture media for growing bacteria. One of Koch's assistants, Richard Petri, developed the petri dish (plate), a container for solid culture media.

Ingredients of Culture Media

Despite its advantages, gelatin was not an ideal coagulant because it was digested by many bacteria and melted when the temperature exceeded 28°C. Agar was unaffected by most bacteria and only melted when it reached a temperature of 100°C.

Agar Agar or Agar

Bacteria and fungi are cultivated either in a liquid (broth) or on a solid (agar) artificial culture medium. She suggested using agar as a thickener - she had been using it successfully for some time to make jellies.

Peptone

A better alternative was offered by Fannie Eilshemius Hesse, the wife of Walther Hesse, one of Koch's assistants.

Other Ingredients

Types of Culture Media

Liquid Media, Semisolid Media, and Solid Media

S ection III Chapter 43Section IChapter 4

Simple, Complex, Deﬁ ned, and Special Media

Isolate bacteria in pure culture and identify the same by performing various tests
Demonstrate biochemical, antigenic, and other phenotypic and genomic properties of the isolated colonies
Demonstrate susceptibility of the isolated bacteria to antibiotics, bacteriophages, bacteriocins, etc
Prepare antigens for various uses
Maintain stock culture

Enriched media: Enriched media are always solid media that encourage the growth of certain fastidious bacteria. In such cases, to isolate Salmonella Typhi and Shigella spp. using enrichment media (such as selenite-F slurry or tetrathionate slurry).

Streak Culture

Lawn Culture

Pour-Plate Culture

Stroke Culture

Stab Culture

Liquid Culture

Anaerobic Culture

Specimen Collection

Culture Media

Anaerobic glove box: The anaerobic glove box is another innovation developed for isolating anaerobic bacteria. It is

Anoxomat: This is a fully automated system that evacu- ates a portion of the jar contents and refills the jar with

Identification of Bacteria

Morphology of Bacterial Colony on Solid Medium

Growth in Liquid Medium

Biochemical Reactions

Oxidase-positive bacteria include Neisseria spp., Vibrio spp., Aeromonas spp., Plesiomonas spp., Pseudomonas spp., and Moraxella spp. All members of the family Enterobacteriaceae ferment glucose, while glucose and mannitol are fermented by Salmonella spp. be fermented, and glucose and lactose by E.

S ection III Chapter 43Section IChapter 6

Fermentation of glucose only (alkali/acid or K/A reaction; K denotes alkaline reaction and A denotes

Fermentation of lactose and glucose (acid/acid or A/A reaction): Lactose is present in 10 times the amount of

Neither lactose nor glucose fermented (alkali/alkali or K/K reaction): Many Gram-negative, nonenteric bacilli

"IMViC" tests are the most widely used tests in the identification of enteric, gram-negative bacteria. Production of H2S is demonstrated by inoculating bacteria on media containing lead acetate, ferric ammonium citrate, or ferric acetate and incubating overnight at 37°C.

Antigenic Structures

The Voges-Proskauer (VP) test detects the production of acetylmethylcarbinol (acetoin), a natural product formed from pyruvic acid during glucose fermentation. H2S-producing bacteria produce H2S from sulfur-containing amino acids in the medium through their enzymatic action.

Animal Pathogenicity

The acetoin is oxidized in the presence of alkali and atmospheric oxygen to diacetyl which reacts with alpha-naphthol and produces a red color. In this method, a strip of filter paper impregnated with lead acetate is held between the cotton wool plug and the medium in the tube.

Antibiotic Sensitivity

The test is performed by inoculating a broth with glucose phosphate and incubating it at 37°C for 2-5 days. This test is performed by inoculating glucose phosphate broth with the organism and incubating at 37°C for 48 hours.

Typing of Bacterial Strains

The nitrate reduction test is primarily used to identify members of the Enterobacteriaceae family, which usually test positive for the nitrate reduction test. Serotyping: different strains of organisms of the same species can be distinguished based on the difference in the expression of antigenic determinants on the cell surface.

Rapid Identification Methods

Phage type: This has been the basis of strain discrimination and is widely used in epidemiological studies. Genotypic techniques used to differentiate bacterial strains include plasmid profiling and restriction endonuclease analysis of chromosomal DNA.

Molecular Methods

Biotyping: It relies on a set of biochemical reactions to distinguish between different strains within a given species. Bacteriocin typing: This is used in the case of bacterial species for which a number of lytic bacteriophages have been identified.

Bacterial Taxonomy

Bacterial Classification

This type of classification, based on the properties of a large number of properties, is known as numerical taxonomy. Intraspecies classification attempts to subclassify species of a bacterium based on biochemical characteristics (biotypes), antigenic characteristics (serotypes), susceptibility to bacteriophages (phage types), and production of bacteriocins (colicin types).

Nomenclature of Microorganisms

The study of messenger RNA (mRNA) also provides useful information about genetic relationships between bacteria. Genetics is the study of heredity and variation to understand the cause of similarity and differences between parents and their offspring.

Chromosomal Substances

The unit of heredity is the gene, a segment of deoxyribonucleic acid (DNA) that contains in its nucleotide sequence information for a specific biochemical or physiological trait. Bacteria, unlike eukaryotic cells (such as human cells), are haploid (1n), meaning they have a single copy of each gene.

Structure of DNA

Although heredity and variations in bacteria had been observed from the early days of bacteriology, it was not then known that bacteria also obeyed the laws of genetics. It was not until the 1950s that DNA was recognized as the building material of genes.

Structure of RNA

In contrast, eukaryotic cells are diploid (2n); in other words, they have one pair of each chromosome and therefore two copies of each gene. The RNA molecules vary in size from the small tRNAs (which contain fewer than 100 bases) to mRNAs (which can carry genetic messages spanning several thousand bases).

Mutations

Some small RNA molecules (sRNA) function as regulators (a) by binding to the 5' end of an mRNA, preventing ribosomes from translating that message, or (b) by directly base pairing with a DNA strand near the promoter, which prevents transcription. The most common function of RNA is the communication of DNA gene sequences in the form of mRNA to ribosomes.

Types of Mutations

Missense mutation: It is one in which the base substitution results in a codon that specifies a different amino acid to be

Bacterial ribosomes contain three types of rRNA with a size of 2900 bases each and several proteins. Ribosomes containing rRNA and proteins translate this message into the primary protein structure via aminoacyl-tRNA.

Nonsense mutation: It is another type of mutation in which the base substitution produces a terminal codon that

For example, the 23S RNA in the 50S ribosomal subunit catalyzes peptide bond formation during protein synthesis. For mRNA synthesis, DNA acts as a template; therefore, adenine, guanine, cytosine and uracil in mRNA become complementary to thymine, cytosine, guanine and adenine in DNA.

Causative Agents of Mutation

Effects of Mutations

Conditional Lethal Mutation

Extrachromosomal DNA Substances

Plasmids

Nontransmissible plasmids: These cannot be transferred from cell to cell, because they do not contain the transfer

The F factor: The F plasmid, also called F factor, is a transfer factor that contains the genetic information,

Resistance to heavy metals such as mercury and silver mediated by enzyme reductase. They also code for the production of diphtheriacin and pyocyanin produced by Corynebacterium diphtheriae and Pseudomonas pyocyanea, respectively, which are substances similar to colicins.

Transfer of DNA Within Bacterial Cells

In particular, bacteria carrying such genes will show resistance to more than one type of antibiotic, such as penicillins and aminoglycosides. They also carry resistance to some bacteriophages by encoding enzymes, e.g. restriction endonucleases that degrade the DNA of infecting bacteriophages.

Transposons

Large plasmids are conjugative "R" factors that contain additional DNA to code for the conjugation process. The third domain is a repressor gene that regulates the synthesis of both the transposase and the gene products of the fourth domain.

Integrative Conjugative Elements

The first domain is a short DNA sequence of inserted repeats present at the end. These transposons can either cause mutations in the gene into which they insert or alter the expression of nearby genes.

Programed Rearrangements

It causes mutation by moving from one end to another in DNA sequence and is believed to control various cellular responses.

Transfer of DNA Between Bacterial Cells

Transformation

Transduction

Specialized transduction results from lysogenization of the recipient bacterium by specialized transducing phage and expression of donor genes. Specialized transducing phages are rare recombinants that lack part of the normal phage genome.

Conjugation

They contain a part of the bacterial chromosome that is present next to the prophage attachment site. In mating between Hfr and F⫺ strains, the F plasmid segment containing the tra region is transferred last after the entire bacterial chromosome has been transferred.

Recombination

In this process, the single strand of DNA entering the recipient F⫺ cell contains part of the F factor at one end, followed by the bacterial chromosome and then by the rest of the F factor. The plasmid responsible for drug resistance consists of two components, namely the RTF and a resistance determinant(s) for each of the several drugs.

DNA: An Amazing Molecule

Genetic Engineering

Preparation of DNA Fragments with Restriction Enzymes

Physical Separation of Differently Sized DNA Fragments

Enzymes for Dicing, Splicing, and Reversing Nucleic Acids

Restriction fragment length polymorphisms: The pieces of DNA produced by restriction endonucleases are called restriction fragments. Cloning these fragments makes it possible to isolate the flanking regions of the DNA by a technique known as chromosomal walking.

Nucleic Acid Probes

Polymerase Chain Reaction

Also, PCR can quantitate DNA products without the use of isotopes. This allows one to find the initial amount of

As mentioned earlier, the target DNA to be amplified is normally less than about 5000 bp in length.

As mentioned earlier, the target DNA to be amplified is normally less than about 5000 bp in length. A long PCR

Multiplex PCR is another modification of PCR in which two or more target sequences can be demonstrated simultane-

Several commercial instruments are available that combine PCR amplification of target DNA with detection of amplicons in the same sealed container. They complement conventional antimicrobial susceptibility testing for the detection of methicillin resistance in staphylococci, rifampicin resistance in M.

Recombinant DNA Technology

PCR and other molecular techniques have already proven exceptionally valuable in many areas of molecular biology, medicine and biotechnology. Diagnose AIDS, Lyme disease, chlamydia, tuberculosis, hepatitis, human papillomavirus and other infectious agents.

Cloning Vectors and Hosts

The results are semi-quantitative and can be obtained in much less time than it takes to perform a conventional PCR assay.

Biological Products of Recombinant DNA Technology

Genetically Modified Organisms

Gene Therapy

Antimicrobial drugs (also called anti-infective drugs) are a special class of compounds that can destroy or inhibit microorganisms even in high dilutions. Synthetic antimicrobial drugs are obtained in the laboratory from dyes or other organic compounds through chemical reactions.

Mechanisms of Action of Antimicrobial Drugs

Inhibition of cell wall synthesis 2. Inhibition of protein synthesis

When chemotherapeutic drugs are given as a means of controlling infection, the practice is called antimicrobial chemotherapy. Although the division into these two categories is traditional, they tend to overlap because most antibiotics, called semi-synthetic antibiotics, are now chemically modified in the laboratory.

Inhibition of Cell Wall Synthesis

Prophylaxis and treatment of serious infections caused by Gram-positive bacteria, including MRSA and Enterococcus faecalis. Treatment of pseudomembranous colitis and Clostridium difficile-associated diarrhea, with comparable efficacy to vancomycin.

Inhibition of Protein Synthesis

Carbapenems (such as imipenem) and monobactams (such as aztreonam) are other examples of lactam antibiotics, but these are structurally different from penicillins and cephalosporins. Vancomycin is a glycopeptide, but its mode of action is very similar to that of -lactam antibiotics such as penicillins and cephalosporins.

Inhibition of Nucleic Acid Synthesis

Alteration of Cell Membrane Function

Resistance to Antimicrobial Drugs

Mechanisms of Antibiotic Resistance

Some bacteria develop resistance to antibiotics by changing their permeability to the drug in such a way that an effective intracellular concentration of the antibiotic is not obtained within the bacterial cell. Efflux pumps have been found to be responsible for conferring resistance to many classes of antibiotics, including aminoglycosides, quinolones, etc.

Basis of Resistance

Nongenetic basis 2. Genetic basis

This can be partially overcome by the simultaneous presence of a cell-active agent, e.g. penicillin. Bacteria can develop resistance by changing metabolic pathways that bypass the response inhibited by the drug.

Nongenetic Basis of Resistance

Certain bacteria under ordinary circumstances are usually killed by penicillins. But these bacteria, if lose their cell
In certain conditions, such as in the abscess cavity, bacteria can be walled off, which prevents drugs to penetrate effec-
Presence of foreign bodies (such as surgical implants and cath- eters) and penetration injury caused by splinters and sharpen-
Nonreplicating bacteria in their resting stage are less sensi- tive to the action of cell wall inhibitors such as penicillin

The largest family of bacterial efflux pumps includes ABC (ATP-binding cassette) multidrug efflux pump, multidrug resistance and toxic compound extrusion (MATE) efflux pumps, major facilitator superfamily efflux (MFSE) pumps, etc.

Genetic Basis of Drug Resistance

Treatment of tuberculosis with two or more antituberculosis drugs is carried out to prevent the development of multidrug resistance in tuberculosis. R factors: These are circular double-stranded DNA molecules that carry the genes responsible for resistance to various antibiotics.

Specific Mechanisms of Resistance

Production of penicillin-destroying enzymes ( ␤ -lactamases)
Mutation in genes coding for PBP: This form of resistance occurs due to the absence of some penicillin receptors (PBP)
Reduced permeability to drug: Low-level resistance of Neisseria gonorrhoeae to penicillin is caused by poor permeabil-
Plasmid-dependent resistance to aminoglycosides enzymes is the most important mechanism. It depends on the
Chromosomal resistance of microbes to aminoglycosides is the second mechanism. Chromosomal mutation in genes

Resistance to trimethoprim is caused by a chromosomal mutation in the gene encoding dihydrofolate reductase, an enzyme that reduces dihydrofolate to tetrahydrofolate. Bacteria develop resistance due to a mutation in the gene that codes for DNA-dependent RNA polymerase.

Antibiotic Sensitivity Testing

Disc diffusion tests 2. Dilution tests

The bacteria develop resistance due to mutation in the gene encoding arabinosyltransferase, which synthesizes arabinogalactan in the mycobacterial cell wall. Pyrazinamide resistance is due to mutation of the gene encoding bacterial amidase, which converts it to its active form, pyrazinoic acid.

Disc Diffusion Tests

Kirby–Bauer disc diffusion method 2. Stokes disc diffusion method
Proteus mirabilis, Proteus vulgaris, and other bacteria producing swarming produce a thin film on agar surface often extend-
Many strains of MRSA grow very slowly in the presence of methicillin. They produce growth within the zone of inhi-
Penicillinase producing strains of Staphylococcus often fail to secrete enough enzymes to neutralize penicillin close to
Trimethoprim and sulfamethoxazole should be tested separately to know whether the bacterium is sensitive to

The result is reported by comparing the zones of inhibition of the test and control bacteria. In such situations, the zone of inhibition should not be considered, and resistant should be reported regardless of the size of the zone.

Dilution Tests

Broth dilution method 2. Agar dilution method

The concentration at which bacterial growth is completely inhibited is considered the MIC of the antibiotic. The MIC is read from the rock at the intersection of the zone with the tape.

Antibacterial Assays in Body Fluids

The strip is placed on the agar plate inoculated with the test organism with the MIC scale facing the opening side of the plate. E-test is a very useful test for easy interpretation of the MIC of an antibiotic (Fig. 9-6).

Types of Microorganisms

Parasites: These are microorganisms that live on a living host and derive nutrition from the host without any benefit to
Pathogens: A microorganism capable of causing disease, especially if it causes disease in immunocompetent people, is
Opportunistic pathogens: A microbe that is capable of causing disease only in immunocompromised people is known
The first and foremost being that the primary pathogens regularly cause overt disease, whereas opportunistic ones
Long-term survival of a microbe is another difference

The relationship between host and parasite is determined by the interaction between host factors and the infecting microorganisms. The outcome of any microbial infection depends on the interaction between the host and the parasite.

Infection

There is an element of symbiosis in the relationship between the human host and the intestinal flora; humans provide bacteria with a warm, moist environment for their survival, and the gut flora provides a natural barrier against many invading pathogens. They are present as bacterial flora of the skin and mucous membranes, including the upper respiratory tract, lower gastrointestinal tract and vagina.

Types of Infections

Stages of Pathogenesis of Infections

The ability of the organism to break host barriers and to evade destruction by innate local and tissue host defenses

The ability of the organism to replicate, to spread, to estab- lish infection, and to cause disease

The ability of the organism to transmit to a new susceptible host

The innate and adaptive immunologic ability of the host to control and eliminate the invading microorganism

Transmission of Infection

Humans: Humans are the most common sources of infections caused by the microorganisms. They may be either
Animals: Animals are also important sources of infection for humans. The symptomatic as well as asymptomatic animals
Food: Food items contaminated with pathogens also act as source of infection and cause diarrhea, dysentery, food poison-
Water: Water contaminated with microorganisms also acts as a source of infection and transmits water-borne diseases, such as
Contact: Transmission of microorganisms from person to person occurs by direct or indirect contact. Transmission by
Inoculation: Infections can be transmitted by inoculation of microorganisms directly into tissues of the host. For
Inhalation: Infections are transmitted by inhalation of droplet nuclei that are discharged into the air by coughing,
Vectors: Mosquitoes, flies, fleas, ticks, mite, and lice are the vectors that transmit many diseases as mentioned earlier

Influenza, tuberculosis, and some superficial fungal infections are examples of fomite-borne diseases. Inoculation: Infections can be transmitted by inoculation of microorganisms directly into host tissues.

Entry of Organisms and Evasion of Local Defenses

Adherence to Cell Surfaces

For example, many adhesion proteins are present at the tip of the pili of E. These bind specific receptors on the surface of the urinary bladder to initiate urinary tract infections.

Growth and Multiplication of Bacteria at the Site of Adherence

Enzymes: Invasion of bacteria is enhanced by many enzymes
Antiphagocytic factors: Many bacterial pathogens are rapidly killed once they are ingested by polymorphonuclear
Bioﬁ lms: The bioﬁ lm is an aggregate of interactive bacteria attached to a solid surface or to each other and encased in
Inﬂ ammation: Inﬂ ammation is an important host defense induced by the presence of bacteria in the body. It is of two
Intracellular survival: A few mechanisms that are suggested for intracellular survival of bacteria include
Exotoxins: Exotoxins are heat-labile proteins that are pro- duced by several Gram-positive and Gram-negative bacteria
Endotoxins: The term endotoxin was coined in 1893 by Pfeiffer to distinguish the class of toxic substances released

They are heat stable and are released from the bacterial cell surface by cell wall breakdown. For example, immune complexes deposited in the kidney glomeruli cause poststreptococcal glomerulonephritis.

Manifestations of Disease

In certain diseases, the symptoms are not caused by the organism itself, but as a result of immune response to the presence of organisms. Similarly, the host's immune response is an important cause of disease symptoms in patients suffering from syphilis caused by T.

Termination of Disease

Stages of an Infectious Disease

Incubation period: This denotes the time interval between the entry of infective agent and the onset of clinical mani-
Prodrome period: It is the time during which only non- speciﬁ c symptoms of disease occur
Speciﬁ c illness period: The time during which the charac- teristic features of disease occur
Recovery period: The time during which symptoms resolve and health is restored

The first European mention of immunity is recorded by Thucydides in Athens in the fifth century BC. Once the concept of the existence of immunity was established, it was not long before manipulation of immunity under controlled conditions followed.

Types of Immunity

First, it was Edward Jenner who, in a successful experiment, injected material from a cowpox pustule into the arm of an 8-year-old boy and demonstrated the lack of disease development after subsequent exposure to smallpox. Von Behring and Kitasato showed that serum (the liquid, non-cellular component of clotted blood) from animals previously immunized against diphtheria could transfer the immune state to non-immunized animals.

Innate Immunity

Factors that may influence innate host immunity include the age and nutritional status of the host. The ability of the host to immediately recognize and combat invaders displaying such molecules is a strong feature of innate immunity.

S ection II Chapter 11

Adaptive (Acquired) Immunity

Humoral immunity: Mediated by molecules in the blood and mucous secretions called antibodies. However, once active immunity develops, it is long-lasting and this is the main advantage of active immunity.

Local Immunity

Natural passive immunity: It is observed when IgG is transferred from mother to fetus during pregnancy. Natural passive immunity is also observed by the passage of IgA from mother to newborn during breastfeeding.

Herd Immunity

When immunity is conferred by the transfer of serum or lymphocytes from a specifically immunized individual, this is known as passive immunity. Artificial passive immunity: This is induced in an individual by administration of preformed antibodies, usually in the form of antiserum, raised against an infectious agent.

Determinants of Antigenicity

Molecular size 2. Foreignness

Molecules that can be recognized by the immunoglobulin receptor of B cells or by the T cell receptor when complexed with a major histocompatibility complex (MHC) are called antigens. All molecules that are immunogenic are also antigenic, but not all antigenic molecules can be considered immunogenic.

Chemical-structural complexity 4. Stability

Antigens that are not immunogenic but can participate in immune reactions are called haptens. The term immunogenicity means the ability of an antigen to cause an immune reaction in the form of a B-cell or T-cell response, while the term antigenicity only means the ability to combine specifically with the products of the above responses.

Other factors

Molecular Size

Chemical-Structural Complexity

Stability

S ection II Chapter 12

ANTIGEN 91

Other Factors

Antigenic Specificity

Epitopes

Pieces of the bacteria are then processed and presented in the context of class II MHC molecules. Processing of endogenously derived antigens: In this process, viral proteins synthesized in a cell are processed and then presented in the context of class I MHC molecules.

Species Specificity

Antigenic determinants are limited to those parts of the antigen that can bind to MHC molecules. Therefore, for a peptide to be immunogenic in a given individual, that individual must have MHC molecules that can bind to it.

Isospecificity

Because the MHC molecules are subject to genetic variability, differences may exist between individuals in their T cell response to the same stimulus. Processing of externally derived antigens: In this process, phagocytosed bacteria are killed and lysed by phagocytic cells, such as macrophages.

Isoantigens

Histocompatibility Antigens

Autospeciﬁ city

Organ Speciﬁ city

Heterophile Speciﬁ city

ANTIGEN 93

The Paul-Bunnell test is used for the diagnosis of infectious mononucleosis caused by Epstein-Barr virus infection by demonstration of heterophilic antibodies agglutinating sheep erythrocytes. A cold agglutinin test is performed for the diagnosis of primary atypical pneumonia caused by Mycoplasma pneumoniae by detecting heterophile antibodies.

Haptens

Weil-Felix reaction is a test used for the diagnosis of rickettsial infections, in which the strains of Proteus species (such as OX 19, OX 2 and OX K) are used to detect heterophilic antibodies produced against rickettsial pathogens .

Superantigens

They prevent attachment of microbes to mucosal surfaces of the host
They reduce virulence of microbes by neutralizing toxins and viruses
They facilitate phagocytosis by opsonization of microbes
They activate complement, leading to complement-mediated activities against microbes

Antibodies are globulin proteins (immunoglobulins) synthesized in serum and tissue fluids that specifically react with the antigen that stimulated their production. Antibodies are one of the main plasma proteins and are often called the "first line of defense" against infections.

Immunoglobulins

In 1891, Tizzoni and Cattani named the unknown substance present in the serum "antitoxin" that provided protection during transmission. They demonstrated that hyperimmunization increases the concentration of β-globulins in the serum and that this fraction contains antibody activity.

Structure of Immunoglobulins

Von Behring and Kitasato performed the first experiments that proved the physical existence of antibodies in 1890. The World Health Organization (WHO) in 1964 coined the term "immunoglobulin (Ig)" for the term antibody.

S ection II Chapter 13

ANTIBODIES 95

Treatment of Immunoglobulins with Proteolytic Enzymes

Immunoglobulin Antigen Determinants

Heavy chains are distinguished by the presence of heavy chain markers such as , , , and in the immunoglobulins IgM, IgG, IgA, IgD, and IgE, respectively. The allotype refers to allelic differences in both the variable and constant regions of immunoglobulin.

Biosynthesis of Immunoglobulins

The isotype of an immunoglobulin refers to the particular constant region of the light or heavy chain of the immunoglobulin. Allotypes are present in some but not all members of a species and are inherited in a simple Mendelian fashion.

Metabolism of Immunoglobulins

These are Am on heavy chains, Gm on heavy chains and Km on light chains.

Immunoglobulin Classes

IgG1, IgG3, and IgG4 are special because these are the only immunoglobulins with the ability to cross the placen-
IgG3, IgG1, and IgG2, in order of their efficiency, are effective in the activation of the complement
ANTIBODIES 97

IgG1 and IgG3 bind with high affinity to Fc receptors on phagocytic cells and thus mediate opsonization. IgG4 has

ANTIBODIES 99

There is only a 5% difference in amino acid sequence among human chain isotypes, excluding the hinge region. A cysteine residue occurring at the penultimate position of a carboxy-terminal region of the chain forms a disulfide bond that joins the J-chain.

Abnormal Immunoglobulins

Since these reactions are essentially specific, they have been used in many diagnostic tests to detect either the antigen or the antibody in vitro. The antigen and antibody responses also form the basis of immunity against microbial diseases in vivo.

General Features of

Antigen–Antibody Reactions

Physicochemical Properties

Affinity

Avidity

Specificity

Cross-Reactivity

Stages of Antigen–Antibody Reactions

Primary Stage

Secondary Stage

Types of Antigen–Antibody Reactions

Precipitation

S ection II Chapter 14

Precipitation in solution 2. Precipitation in agar

Precipitation in agar with an electric field

Radial immunodiffusion has been used for quantitative estimation of antibodies and antigens in serum. The height of the rocket, measured from the well to the tip, is directly proportional to the amount of antigen in the sample (Fig. 14-8).

Agglutination

These particles can be coated with antibodies to detect antigen in the serum and other body fluids. When RBCs are coated with antigen to detect antibodies in the serum, the test is called indirect hemagglutination (IHA) test.

Complement-Dependent Serological Tests

Complement fixation test 2. Immune adherence test

Detection of amoebic and hydatid antigens in the serum for the diagnosis of amoebiasis and cystic echinococcosis, respectively; And.

Cytolytic or cytocidal reactions

If the red cells lyse, this indicates that there were no antigen-specific antibodies in the patient's serum. This forms the basis of the test used to measure anti-cholera antibodies in serum.

Neutralization Tests

In a positive test, if the serum contains antibodies, the antigen would have been used in the first test, the standard antiserum added subsequently will fail to fix complement, thus causing hemolysis. If the horse's complement was used up by the antigen-antibody reaction in the first step, agglutination of the sensitized cells does not occur.

Opsonization

The indirect immunofluorescence test is used for the detection of specific antibodies in serum and other body fluids for the serodiagnosis of many infectious diseases. The first step in the indirect immunofluorescence test is the incubation of a fixed antigen (e.g., in a cell or tissue) with unlabeled antibody, which becomes associated with the antigen.

Immunofluorescence

Direct immunofluorescence test 2. Indirect immunofluorescence test

The test sample containing the suspected antigen is added to the wells and allowed to react with the antibodies in the wells. The chromogenic reaction is then compared to a standard curve to determine the exact amount of antigen present in the test sample.

Enzyme Immunoassays

On the other hand, if the specific antibody were not present in the sample, there would be no complex formation. In a negative test, where there are no antibodies present in the serum, antigen in the coated wells is available to combine with enzyme-conjugated antibodies and the enzyme acts on the substrate to produce color.

Radioimmunoassay

Principle of the test is that two specific antibodies, one conjugated with enzyme and the other present in test serum (if serum is positive for antibodies), are used. The test can be used to determine very small amounts (eg nanograms) of antigens and antibodies in the serum.

Western Blotting

A standard curve is constructed by plotting the percentage of antibody-bound radiolabeled antigen against known concentrations of a standardized unlabeled antigen, and the antigen concentrations in patient samples are extrapolated from that curve. The major disadvantages of the RIA are: (a) the cost of equipment and reagents, (b) the short shelf life of radiolabeled compounds, and (c) the problems associated with the storage of radioactive waste.

Chemiluminescence Assay

These are the types of antigen-antibody reactions that are visualized directly through an electron microscope. The complement system, which is an important part of the human host immune system, consists of approximately 20 proteins present in normal human serum.

The Complement System

The term complement refers to the ability of a system of certain non-specific proteins in normal human serum to complement, ie. they increase the effects of other components of the immune system, such as antibodies.

Properties of Complement

It is present in sera of all mammals including humans and in lower animals including birds, amphibians, and fishes

These are heat-labile substances that are inactivated by heating serum at 56°C for 30 minutes

These are glycoproteins and are synthesized primarily by liver cells and to a very less extent by macrophages and

The complement usually does not bind to the antigen or antibody but only to antigen–antibody complex

The importance of the complement lies in the fact that it contributes to both the acquired and innate immunity of

Nomenclature of Complement

Activation of Complement

The classical pathway 2. The alternative pathway

Classical Pathway of Complement Activation

Activation of C1 is the first step in the cascade of classical pathway activation. The C1 actually is a complex of three
C1q binding in the presence of calcium ions leads to activation of C1r and C1s. Activated C1s is an esterase
The C3 convertase activate thousands of C3 molecules and splits these molecules into C3a and C3b. A single
The C5b–8 complex on binding to C9 molecules under- goes polymerization, which finally ends in the forma-

All three pathways converge at the step involving the formation of the MAC. C8, upon binding to the complex, stabilizes the attachment of the complex to the foreign cell membrane.

Alternative Pathway of Complement Activation

The C3bB is split into two fragments, Ba and Bb, by another serum protein called factor D or C3 proactive convertase

Ba is released into the medium and Bb binds to C3b to form the C3bBb complex, which possesses the C3 convertase activity. The C3bBb complex activates more C3, leading to the formation of more C3bBb, which in turn is able to activate.

The C3bBb complex activates more C3, leading to the for- mation of more C3bBb, which in turn is capable of activat-

Since factor D has never been isolated in its proenzyme form, it is generally believed that it is activated immediately when it leaves the hepatocyte where it is synthesized.

The alternative pathway then proceeds from C3 to produce finally the MAC, in the same way as occurs in the classical

Lectin Pathway of Complement Activation

Regulation of Complement System

Level of antibody: The level of antibody itself is the ﬁ rst regulatory step in the classical pathway. If antigen is not bound
C1 inhibitors: These inhibitors play a critical role in limiting unnecessary complement activation. These prevent
Other inhibitory substances: Multiple substances have inhibitory effects over different steps of the activation sequence
Decay-accelerating factor (DAF): It is another inhibitory substance located in a large variety of host cell membranes

If the antigen is not bound to the antibodies, the complement binding sites on the heavy chains of IgG and IgM are inaccessible to the C1 component of complement. The C1 inhibitors can also help remove the entire C1 complex from the antigen-antibody complexes.

Biological Effects of Complement

Level of Antibody: The level of antibody itself is the first regulatory step in the classical pathway. Other inhibitory substances: Several substances have inhibitory effects on different steps of the activation sequence. Inhibitory effects on different steps of the activation sequence of the classical pathway.

Chemotaxis

This means that complement is not activated, even though IgM and IgG are present in the blood at all times. Decay-accelerating factor (DAF): It is another inhibitory substance found in a wide variety of host cell membranes.

Hypersensitivity Reactions

However, when antigen binds to specific antibodies, a conformational change occurs that allows the C1 component to bind and initiate the cascade reaction. It is so called because it can accelerate the dissociation of active C4b2a complexes, turning off their ability to activate natural C3.

Cytolysis

These mechanisms probably help to protect the host cells from the possible bystander damage initiated by activated complement fragments (C3b and C4b) formed on and near its surface. It is mediated by the binding of factor H to C3b and cleavage of this complex by specific plasma inhibitor factor I, a protease.

Enhancement of Antibody Production

These prevent the formation and functioning of the C1qrs complex by causing C1 to dissociate from C1qrs. As a consequence, the two types of C3 convertases, C4b2a and C3bBb, are not formed; therefore, the rate of C3 degradation is reduced and host cells are spared from complement-mediated membrane damage.

Deficiency of Complement

Inherited or acquired deficiency of C5–8 components greatly enhances susceptibility to Neisseria bactere-

The synthesis of sufficient quantities of complement is reduced in the patients with severe liver disease, such as

Biosynthesis of Complement

Quantitation of Complement

It consists of lymphoid and reticuloendothelial components and is responsible for the host immune response. The lymphoid cells, including lymphocytes and plasma cells, are responsible for conferring specific immunity.

Lymphoid Tissues and Organs

The lymphoreticular system is a complex organization of cells with diverse morphology, widely distributed in different organs and tissues of the human body, and is responsible for immunity. On the other hand, the reticuloendothelial system, which consists of phagocytic cells and plasma cells, is responsible for non-specific immunity.

Central (Primary) Lymphoid Organs

These cells kill microbial pathogens and other foreign substances and remove them from the blood and tissues.

Peripheral (Secondary) Lymphoid Organs

Chapter 16

Lymphatic Circulatory System

Cells of the Lymphoreticular System

Lymphocytes

Memory cells live for many years or have the capacity to reproduce them
A large number of memory cells are produced, and so secondary response is enhanced and is greater than the
Memory cells are activated by small quantity of antigens and require less costimulation than do the naïve and unac-
Activated memory cells produce greater amounts of interleukins than do naïve T cells when they are first
cell receptor

Regulation of antibody production: Production of anti- bodies by B cells may be (a) T-cell dependent, requiring the
Stimulation of helper and cytotoxic T cells to partici- pate in the CMI: In CMI, the antigen is processed by mac-
Suppression of certain immune responses: T cells have been shown to inhibit several immune-mediated diseases
The cell enlarges 5–10 folds
Its intracellular organelles increase in number and complexity
It acquires increased phagocytic ability
It produces higher levels of hydrolytic enzymes
It begins to secrete a variety of soluble factors
Phagocytosis: Phagocytosis of bacteria, viruses, and other for- eign particles is the most important function of macrophages
Antigen presentation: After ingestion and degradation of foreign materials, the fragments of antigen are presented on

The antibody bound to the surface of the infected cells is recognized by the IgG receptor on the surface of phagocytic cells (eg macrophages, NK cells) and the infected cell is killed. Examples include (a) alveolar macrophages in the lung, (b) histiocytes in connective tissue, (c) Kupffer cells in the liver, (d) mesangial cells in the kidney, (e) microglial cells in the brain, and (f) osteoclasts in the bone.

Major Histocompatibility Complex

They also possess NK T cells, another subset of T cells, which share some functional characteristics with NK cells. The main functions of NK cells are to kill virus-infected cells and tumors.

HLA Complex

Class I: HLA-A, HLA-B, and HLA-C

Class III: Complement loci that encode for C2, C4, and factor B of complement system and TNFs alpha and beta

Biologic Importance of MHC

All these methods are used to determine the haplotype, that is, the class I and class II alleles on both chromosomes of both the donor and recipient. Therefore, a large amount of DNA synthesis indicates that class II (HLA-D) MHC proteins of donor and recipients are not similar.

Humoral Immunity

Log phase: This is the next phase characterized by a steady rise in antibody titers in the circulation

The adoptive immune system is developed in the host primarily to protect the host against harmful effects of pathogens and other foreign agents. There are two main places where pathogens can reside in an infected host: extracellularly in tissue spaces or intracellularly in a host cell; the immune system has different ways of dealing with pathogens at these locations.

Plateau: This is a phase of equilibrium between antibody synthesis and catabolism

Phase of decline: This phase is characterized by an increase in the catabolism of antibodies compared to the production

Primary Response

Secondary Response

Fate of Antigen in Tissues

Production of Antibodies

Chapter 17

Radiometric drugs: These include alkylating agents (such as cyclophosphamide, nitrogen mustard, etc.) that inhibit antibody production. Antimetabolites: These include folic acid antagonists (such as methotrexate); purine analogues (6-mercaptopurine and azathioprine); and cytosine analogs (cytosine arabinose); and uracil (5-fluorouracil).

Monoclonal Antibodies

They are used in transplant surgery and in situations requiring suppression of host immunity. They suppress delayed hypersensitivity, but in therapeutic doses for a short period of time they have little effect on the production of antibodies.

Function of Antibodies

Complement activation: Activation of the complement cascade by antibodies can result in lysis of certain bacteria and viruses. Furthermore, some components of the complement cascade (e.g. C3b) opsonize pathogens and facilitate their uptake via complement receptors on phagocytic cells.

Tests for Detection of Humoral Immunity

Opsonization: Binding of antibodies to a pathogen or foreign substance can opsonize the material and facilitate its uptake and destruction by phagocytic cells. The Fc region of other antibodies interacts with Fc receptors on phagocytic cells, making the pathogen more easily phagocytosed.

Cell-Mediated Immunity

The binding groove of a class I molecule is more restricted than that of a class II molecule; for this reason, shorter peptides are found in class I than in class II MHC molecules. This stimulates Tc lymphocytes to release cytokines, resulting in lysis of target cells.

Cytokines

Transforming growth factor-beta (TGF-␤): It is produced by T cells and many other cell types. Macrophage migration inhibitory factor (MIF): It is produced by macrophages in response to action from endotoxin.

Tests for Detection of CMI

Migration inhibition factor (MIF) test: This test is performed to determine the CMI by making a semiquantita-
Lymphocyte blast transformation: A large number of T cells undergo blast transformation when exposed to certain
Enumeration of T cells, B cells, and subpopulation
Rosette formation: Rosette is a lymphocyte to which three or more sheep erythrocytes are attached. Most T cells form

Tumor necrosis factor (TNF-␣): Produced by activated macrophages in response to microbes, especially lipopolysaccharide from Gram-negative bacteria. IL-3 produced by helper T cells inhibits the growth and differentiation of bone marrow stem cells.

Transfer Factor

Immunological Tolerance

Mechanisms of Tolerance

Clonal deletion: Clones of B and T lymphocytes that recognize self-antigens are selectively deleted in embryonic life,

Clonal anergy: Clonal anergy means a condition in which clones of B and T lymphocytes that recognize self-antigens

Suppression: In this mechanism, clones of B and T lymphocytes expressing receptors that recognize self-antigens are

Types of Immune Tolerance

Immunodeficiency diseases and syndromes are the causes of significant mortality and morbidity, as well as a source of extremely valuable information about the physiology of the human immune system. Immune deficiency can occur in T cells, B cells, complement and phagocytes - the most important components of the immune system.

Primary Immunodeficiencies

Cell Immunodeficiencies

Recurrent infections with certain viruses, protozoa, and fungi indicate T-cell deficiency, while recurrent infections with pyogenic bacteria (such as staphylococci) indicate B-cell deficiency.

Chapter 18

Cell Immunodeficiencies

Combined B-Cell and T-Cell Deficiencies

Complement Deficiencies

This deficiency leads to the continuous action of C1 on C4 to produce more C4a and subsequently more C3a and C5a complement components. An increased production of the vasoactive components, such as C3a and C5a, leads to the production of capillary permeability and edema in the larynx and various other organs.

Phagocyte Deficiencies

Cell Deficiencies

This condition is caused due to defective T-cell signaling that results in failure of IgG production in the body. In case of malnutrition, the synthesis of IgG decreases due to the low supply of amino acids.

Cell Deficiencies

Severe combined immunodeficiency Deficiency of T cells and B cells Defective IL-2 receptor, kinases, recombinases Immunodeficiency with thymoma Impaired cell-mediated immunity, thymus tumor,. Both humoral and cell-mediated arms of the immune response may be involved in hypersensitivity reactions.

Anaphylactic) Hypersensitivity

A hypersensitivity reaction refers to an immune response that results in exaggerated or inappropriate reactions harmful to the host. It is an adverse immune response in which tissue damage occurs due to an exaggerated or inadequate immune response in a sensitized individual upon repeated exposure to the same antigen.

Anaphylaxis

First priming dose (first dose) of antigen is essential, which is necessary to prime the immune system, followed by a shocking dose (second dose) of the same antigen which results in the harmful effects. Gell and Coombs (1963) classified hypersensitivity reactions into four categories based on the time elapsed from exposure of antigen to the reaction and the involved arm of the immune system.

Chapter 19

Atopy

This observation has been used in the past for the diagnosis of passive cutaneous anaphylactic reaction by Prausnitz-Kustner reaction. Prausnitz-Kustner reaction: It is based on the special affinity of IgE antibodies for cells of the skin.

Cytotoxic) Hypersensitivity

In this experiment, serum was collected from Kustner who suffered from a gastrointestinal allergy to certain cooked fish. Radioallergosorbent test (RAST), enzyme-linked immunosorbent test (ELISA) and passive agglutination tests are the commonly used tests for the detection of IgE in the serum for the diagnosis of atopy.

Transfusion Reactions

The same serum was given intradermally to Prausnitz, who then received another intradermal injection of a small amount of prepared fish at the same site 24 hours later.

Erythroblastosis Fetalis

Drug-Induced Hemolysis

Goodpasture’s Syndrome

Rheumatic Fever

Mechanism of Immune-Complex Hypersensitivity

Manifestations of Immune-Complex Hypersensitivity

Immune-Complex Diseases

Autoimmune diseases

Delayed (Cell-Mediated) Hypersensitivity

Mechanism of DTH

Types of DTH Reactions

Positive skin tests for coccidioidomycosis, paracoccidioidomycosis, and other fungal infections indicate exposure to fungi. For both viral and parasitic infections, skin tests are less specific and less useful than serological tests for diagnosis.

Stimulatory Type) Hypersensitivity

A positive test indicates that the person has been infected with the bacteria, but does not confirm the presence of the disease, tuberculosis. More recently, an understanding of the various immunological mechanisms and disorders has led to the same conclusions.

Tolerance

Clonal deletion: The theory of clonal deletion described by Burnet, Fenner, and Medawar based on their studies on

The immune system is a fine-tuned system that works continuously throughout life to protect the body from various foreign cells, whether they are microbes or abnormal cells. Although the immune system is always ready and working, surrounded by its own antigens, it does not react against them.

Pathogenesis of Autoimmunity

Autoimmunity is a condition in which the body produces autoantibodies and immunologically competent T lymphocytes against its own tissues. Ehrlich first postulated in 1901 the existence of tolerance to self-antigens, as well as those situations in which this mechanism would fail, leading to “horror autotoxicus”.

Mechanisms

Release of sequestrated antigens 2. Antigen alteration

Epitope spreading 4. Molecular mimicry

Autoimmune Pathological Process

Autoantibodies: Autoantibody associated diseases are characterized by the presence of autoantibodies in the individ-

Autoantibodies may be directly involved in the pathogenesis of some diseases, while in others they may serve only as disease markers with no known pathogenic role. Autoantibodies play a key role in the pathogenesis of (a) myasthenia gravis, (b) pemphigus vulgaris, and (c) various autoimmune cytopenias.

Immune complexes containing autoantigens: The forma- tion of immune complexes between self-antigens and autoan-

They can also be instrumental in triggering various pathogenic mechanisms leading to tissue damage and cell death. Immune complexes containing autoantigens: The formation of immune complexes between self-antigens and autoantigens.

Autoreactive T lymphocytes: Antigens that are seques- tered from the circulation, and are therefore not seen by the

Animal Models of Autoimmunity

Autoimmune Diseases

Organ-Specific Autoimmune Diseases

This generally causes decreased secretion of mediators and gradual atrophy of the affected organ. Graves' disease: Graves' disease, also known as thyrotoxicosis, diffuse toxic goiter, and exophthalmic goiter, occurs as a result of the production of autoantibodies against the thyrotrophic hormone (thyroid-stimulating hormone [TSH]) receptor (TSH receptor antibodies).

Systemic Autoimmune Diseases

Laboratory studies show increased levels of thyroid hormones (triiodothyronine or T3 and thyroxine or T4), increased uptake of T3, and anti-thyroid receptor antibodies.

HLA Association with Autoimmune Diseases

The replacement of defective organs by transplantation was for many centuries one of the impossible dreams of medicine. The development of strict antiseptic techniques contributes enormously to controlling the infection, while the proper use of immunosuppressive agents and tissue typing increases the success rate of transplantation.

Transplant Immunology

Successful transplantation requires a number of important steps: surgical asepsis; development of surgical techniques of vascular anastomosis; genetic matching of donors with hosts; the use of agents that can suppress the immune system; and prevention of infection in both recipient and donor.

Types of Transplants

Autograft: An autograft is the transfer of individual’s own tissue or organ from one site to another site in the

Allograft: An allograft is the transfer of tissue or an organ between genetically different members of the same species,

Xenograft: A xenograft is the transfer of tissues or organs between members of different species. It represents the

Allograft Rejection

It depends on the similarity in the structure of an intact foreign (allogeneic) molecule and self-MHC molecules. Indirect Presentation: “Indirect presentation” involves the recognition of processed allogeneic MHC molecules, but not of an intact MHC molecule.

S ection II Chapter 21

Transplants of small intestine, lung and even liver - the organs that have a significant amount of lymphoid tissue. GVH reactions occur because the donor T lymphocytes are activated, proliferate, and differentiate into helper and effector cells in the irradiated, immunocompromised host.

Tumor Immunology

The crucial role played by donor T cells is evidenced by the fact that removal of these T cells from a bone marrow transplant prevents GVH reactions. All immunosuppressive drugs used in the prevention and treatment of rejection have been used to treat the GVH reaction.

Features of Malignant Cells

Once cells become malignant, they stop functioning normally and add to the burden on the body by competing
The more “undifferentiated” a cell is, the lesser its functionality and more its malignant nature
They undergo rapid and uncontrolled division
They lose their homing instinct and start invading the basement membrane and enter the vasculature to spread to

The risk of developing a GVH reaction is greatest in the two-month period immediately after transplantation. The initial proliferation of donor T cells occurs in lymphoid tissues, mainly in the liver and spleen, leading to hepatomegaly and splenomegaly.

Tumor Antigens

Tumor-specific antigens

It has been postulated that the immune system is partly responsible for protecting the body against the development of malignant diseases. At the same time, the prevalence of numerous cancers in immunocompetent individuals indicates that the immune system plays only a partial role in protection against malignant diseases and also that it is not very efficient in doing so.

Tumor-associated transplantation antigens

Tumor-associated carbohydrate antigens: They represent abnormal form of mucin-associated antigen detected in breast

Immune Reactions against Tumors

B lymphocytes produce tumor-specific antibodies, which can induce complement-dependent cytotoxicity of tumor cells or mediate ADCC. ADCC can be mediated by a variety of cells expressing Fc receptors (NK cells, monocytes or macrophages, and granulocytes) by recognizing and destroying IgG-coated tumor cells.

Immunosurveillance

Immunotherapy of Cancer

Ehrlich and Morgenroth first described blood groups in goats based on their red cell antigens in an article published in the Berliner klinische Wochenschrift in 1900. The ABO and Rh systems are among the known human blood groups described in the literature.

ABO Blood Group System

Subsequently, Karl Landsteiner, a Viennese pathologist, successfully identified the human ABO blood groups for which he received the Nobel Prize 30 years later. After this initial discovery, blood grouping was developed as a science, and many different systems of grouping were devised based on many isoantigens on the surface of erythrocytes.

ABO Blood Group Antigens

Chapter 22

Rh Blood Group System

Rh Blood Group Antigens

Blood Transfusion

Complications of Blood Transfusion

Hemolytic Disease of Newborn (Erythroblastosis Fetalis)

Fetal–maternal hemorrhage can occur due to trauma, abortion, childbirth, ruptures in the placenta during preg-
The woman may receive a therapeutic blood transfusion with an incompatible blood type. ABO blood group sys-
The third sensitization model can occur in women of blood type O. The immune response to A and B antigens, which
Mother–fetus ABO incompatibility: When the mother and fetus possess the same ABO group, Rh immunization is
Immune unresponsiveness to Rh antigen: Some Rh-negative individuals even after repeated injections of
Number of pregnancies: The risk of hemolytic disease of new born is more in second and successive child, but not in

The RhIG acts by binding any fetal red cells with the D antigen before the mother is able to produce an immune response and form anti-D IgG. However, when Rh and ABO incompatibility coexist, Rh sensitization of the mother is very rare.

ABO Hemolytic Diseases

The mother is also infused with plasma to reduce the circulating levels of antibodies by as much as 75%. These include temperature stabilization, phototherapy, transfusion with compatible packed red blood cells, administration of sodium bicarbonate to correct acidosis, and/or assisted ventilation and exchange transfusion with a blood cell type compatible with both the infant and the mother.

Properties of the Bacteria

The family Micrococcaceae consists of Gram-positive cocci, which are aerobic and anaerobic, and are arranged in tetrads or clusters. The other important human pathogens are coagulase-negative staphylococci (CONS), including Staphylococcus epidermidis, Staphylococcus saprophyticus, Staphylococcus haemolyticus, Staphylococcus hominis, Staphylococcus warneri, Staphylococcus saccharolyticus, Staphylococcus schleiferi and Staphylococcus lugdunensis.

Chapter 23

Selective media: Mannitol salt agar, milk agar, and glycerol monoacetate agar are the commonly used selec-

S ection III Chapter 23

Cell Wall Components and Antigenic Structure

Pathogenesis and Immunity

Hyaluronidase: The enzyme hyaluronidase hydrolyzes the acidic mucopolysaccharides present in the matrix of the connective tissue, thereby facilitating the spread of bacteria in tissues. Coagulation of plasma is caused by the action of the enzyme coagulase secreted by the pathogenic strains of S. The enzyme coagulase is of two types: a) free coagulase and (b) bound coagulase.

Clinical Syndromes

The toxin breaks intercellular bridges in the stratum granulosum of epidermis and causes it to separate from the underlying tissue, leading to a blistering and exfoliating disease of the skin. It causes marked necrosis of the skin and hemolysis by damaging the cell membrane, which leads to the release of low-molecular-weight substances from the damaged cells.

Complications of Staphylococcal Diseases

STSS is a multisystem disease characterized by fever, hypotension, myalgia, vomiting, diarrhea, mucosal hyperemia, and an erythematous rash followed by desquamation of the skin, especially on the palms and soles. It is associated with extensive exfoliation of the skin, where the outer layer of the epidermis is separated from the underlying tissue and is characterized by the appearance of extensive bullae.

Epidemiology

Such plates are then incubated overnight at 30°C and observed for the presence or absence of colony lysis by the phages. The phage type of a strain is known by determining the phages that lyse it.

Laboratory Diagnosis

Using this method, most strains of staphylococci can be classified and divided into five lytic groups, but a few cannot be classified and form an unclassified group (Table 23-5). The test is performed by mixing a thick suspension of staphylococci with a loop of undiluted rabbit plasma on a glass slide.

Treatment

Plasmid-mediated resistance: This type of resistance may be due to the production of enzyme penicillinase (beta- lactamase),

The plasmids also carry markers of resistance to heavy metals, such as arsenic, cadmium, mercury, lead and bismuth, as well as to other antibiotics, such as erythromycin and fusidic acid. MRSA strains can be treated with glycopeptide antibiotics such as vancomycin and teicoplanin in severe systemic infections, such as pneumonia, bacteremia and endocarditis.

Prevention and Control

Reduced affinity of penicillin-binding proteins (PBP; present in the staphylococcal cell wall) to beta-lactam antibiotics also contributes to bacterial resistance to penicillins and other beta-lactam antibiotics. Proper hand washing and the use of topical agents such as mupirocin and chlorhexidine on the skin and nose to eradicate the agents are effective in preventing and controlling nosocom